famguy,
The main bearing bulkheads are the area of concern. I've heard before, the alloy issue of less nickel as sirdragon says, but have no real evidence of that. We hear that about certain 350 Chevy blocks, too, and that has turned out to be an "urban myth". This is not to dispute what he said, just to clarify. If anyone knows of a real "study" where the alloys were analyzed, I would be most interested in reading it.
6X-8s are an excellent place to start for a 461 or 467 "stroker". If you keep power levels under 550 HP or so, your block shoould be fine.
We like the Eagle kit the best. Others will tell otherwise. Ask "Why?" Get clear and concise answers. If they say the Eagle isn't "good", run away!!! If they say they market their own "kit", ask about the specific compononents. At least one Pontiac vendor out there will tell you his stuff is better because his pistons don't require a support rail for the oil ring. Ask why that's better, or more importantly, ask why a support rail is "bad". We've been using them in small block race engines for over 30 years, before "stroker" Pontiacs became popular. Never saw one "fail".
In any case, if the vendor is at all vague or offering evasive answers, go elsewhere. If the word "perfect" is used to describe certain parts, go elsewhere (nothing man-made is perfcect).
There many good Pontiac shops out there, of which Butler Performance is one.
FWIW
Jim